Thin glass sheets with an alkali-free composition are known to have exceptionally high dielectric breakdown strength (12 MV/cm) and electrostatic energy density values as high as 38 J/cm3.1 A key factor in achieving reproducible dielectric breakdown results for glasses is the sample thickness and surface condition. In the past, thin Pyrex sheets with high characteristic breakdown strength (9 MV/cm) and narrow breakdown distribution have been fabricated by blowing glass tubes and etching with hydrofluoric (HF) and hot chromic acids.2 Similarly, dielectric breakdown strengths as high as 7 MV/cm have been reported for thin silica glass and quartz samples (50 μm) that were prepared by polishing in a manner that avoided the formation of microcracks.3 Flat panel display glass production processes can provide commercially available glass sheets that are thin (e.g. 10-700 μm), defect-free and which possess flat, smooth pristine surfaces. As such, this type of glass has the potential to serve as high energy density capacitor materials for portable or pulsed power applications. Glass capacitors also have significant commercial potential for electric vehicles. The on-board electric power distribution systems require high temperature capacitors that operate reliably over 10 to 15 years.
A number of dielectric breakdown mechanisms have been proposed for amorphous oxides and the thickness of the oxide is known to play a key role in breakdown events that are mediated by thermal, electrical, and mechanical contributions.4 In addition, breakdown processes originate with the creation of a critical quantity of high-mobility charges that increase over time. Breakdown is generally associated with regions of high local electric field originating from surface and bulk defects, microstructural inhomogeneities and space charges. Regardless of the initial breakdown mechanism, there is an increase of electrical conductivity followed by various phases of dielectric breakdown.
The dielectric thickness influences all phases of the breakdown sequence and both intrinsic and extrinsic breakdown mechanisms have a thickness dependence. Avalanche or catastrophic breakdown, initiated by current injection from a cathode, is inversely proportional to thickness.5 Thermal breakdown is an interchange between joule heating and temperature dependent conductivity with the breakdown strength increasing as thickness decreases due to enhanced heat transfer to the ambient environment. The effect of porosity on dielectric breakdown has been extensively studied analytically for a uniform pore size distribution in a homogeneous dielectric and with Monte Carlo simulations which have shown that the breakdown strength is related to the pore size, distribution of pore sizes and the ratio of pore size to dielectric thickness.6,7 
Appreciating that defects and/or failures can and do occur, self healing capacitor structures are designed such that metal electrodes recede from a channel in the dielectric layer at a fault site (so-called graceful failure). As a result, the capacitor remains operational with only a slight decrease in the capacitance value. Self healing has been observed for silicon and tantalum oxide dielectrics with aluminum electrodes having a layer thickness of less than 2000 Å.8 Self healing in polymer film capacitors has been widely studied for dielectric layer thickness in the range of 1 and 20 μm.9 The primary condition for self healing is that the electrostatic energy dissipated in the fault regions is sufficient to vaporize a metal electrode area around the fault channel.
However, heretofor self healing capacitor structures have yet to meet all of the requirements for successful commercial implementation (e.g. cost, temperature, reliability, etc.). Therefore, a self clearing high energy glass capacitor that affords desired self healing and reasonable cost would be desirable.